Grinding wheel



April A28, 1942- I.. H. MILLIGAN ET AL 2,281,525

GRINDING WHEEL A Filed Nov. 19, 1956 FG. '7 ff) 37 .27 zfa/ f K/ 44 a lI f I "-15.15 f' l I E 5f Ham 2.6 27 22a I /554 22a 22o w 3 31 ma 25 Il|1 w11 25 2 ROBERT H. LQMBARD Patented pr. 1128, v1942 GRIN DING WHEELLowell H. Milligan and Robert H. Lombard,l

Worcester, Mass., assgnors to Norton Company, Worcester, Mass., acorporation of Massachusetts Application November 19, 1936, Serial No.111,720

(ci. 51293 t lower hydraulic press plungers, being the same y Claims.

The invention relates to grinding wheels and `methods for themanufacture thereof, and with regard to its more specific features tothe manufacture of diamond abrasive wheels bonded with vitried ceramicbond.

One object of the invention is to provide a vitried diamond grindingwheel of relatively large diameter and reasonable cost. Another objectof the invention is to prdvide a method for the manufacture of anarticle of the class indicated. Another object of the invention is topermit the manufacture of a medium to large sized grinding wheelcontaining diamond abrasive at a reasonable cost, more especially usingvitriable or ceramic bond. Another object of the invention is to make agrinding wheel of two-part construction which nevertheless acts as anintegral unit so far as many physical characteristics are concerned.'Other objects will be in part obvious or in part pointed outhereinafter.

'Ihe invention accordingly consists in the features of construction,combinations of elements,

arrangements of parts, and in the several steps and relation and orderof each of said steps to one or more of the others thereof, all as willbe illustratively described herein, and the scope of the application ofwhich will be indicated in the y granular material and vitriiied ceramicbond, ally` just after stripping from the mold ring.

y Figure 2 is a view of the parts and material shown in Figure 1, withthe central plug pushed downwardly and out of the top mold plate.

Figure 3 is a view similar to Figure 2, the top mold plate having beenremoved.

Figure 4 shows the foregoing parts turned over and a different bottomplate in position thereunder.

Figure 5 shows the next step comprising the pressing of the plug intothe new bottom plate.

Figure 6 shows the parts after the erstwhile bottom plate has beenremoved.

Figure 7 is a fragmentary view illustrating a portion of the apparatusfor the second molding operation and showing the assemblage of Figure 6located therein.

Figure 8 is a radial cross section through the entire mold for thesecond molding operation and its supporting structure, showing alsoupper and apparatus a fragment of which is shown in Fig;

ure 7, however Figure step in the method.

Figure 9 is a further fragmentary View of the apparatus of the Figures 7and 8, but showing the upper hydraulic press plunger elevated and the 8showing a subsequent moldfor thesecond molding operation about 'to to acentral disk 22 having a central hole 23,

which disk, so far as certain features of the invention are concerned,may be of. any substance' having adequate strength but, so far as theprei ferred form of the invention is concerned,'com

`prises granular material bonded with ceramic vitried bond, the entirewheel being vitried or burned in a. kiln in a, single firing operation.To produce this integral wheel 20, the multi-stage y molding andpressing operations herein disclosed and indicated in the drawing arepreferably used. It is desired that the shrinkage characteristics of thediamond part 2l and the non-diamond part 22 be the same or as nearlyalike as possible. It is further desired that the coefficient ofexpansion ofthe granular part in the part 22 be as nearly as may be thesame as that of the diamonds in the part 2l, all in order that thenished product shall have physical characteristics as nearly as possiblethose of a monolith so as to avoid breakage in use or otherwise.

Diamonds to be used as abrasive grains in the manufacture of bondedabrasive products are so expensive as to limit their use, in products.of relatively large size, to an exterior or peripheral zone lthat is tobe actually employed for the grinding orcutting operation itself, andwhich peripheral zone can be completely used up with a minimum wastage,in the normal grinding operations for which the article is used. We havefound that for many practical grinding operations diamonds can .be mosteffectively bonded with a ceramic bond. Because diamonds are oxidizable,we prefer to use low ring temperatures. While the present invention isnot limited to any specific bond, nevertheless in order to disclose thebest way now known to us of carrying our invention into actual practice,we note that the bond used may be such as disclosed in our priorcopending application Serial No. 51,334 filed November 23, 1935. Astherein disclosed, the bond for the diamonds may comprise the following:

Bonds according to both of these examples are soft at in theneighborhood of l000 C.

Still considering preferred examples of the best manner of carrying theinvention into practice, we may take four parts by weight of diamondbort of 100 meshfgrit size and one part by weight of any of the aboveceramic mixtures. We add thereto 4% of the whole of a. 4% solution -ofGlutoline as a temporary binder, to plasticize the mass and to give itsufficient green' strength,

Placing this mixture aside, we make an exact- I ly similar mixture ofbond and granular material which in the preferred form of the inventionis vitreous silica (Sion), preferably of the same grit size as that ofthe diamonds, in the illustrative example` 100 grit size. The proportionby volume of bond to silica should be the same as thel proportion byvolume of bond to diamonds. The amount of this second non-diamondcontaining mixture is calculated to have a volume, when'compressed, thatof the disk 22, and likewise the volume of the diamond containingmaterial is calculated to have the volume, when pressed, of the annulus2 The volume of these parts may be readily calculated geometrically andthe total weight for a given volume will trai hole. Therefore, we pressthe plug 21 downwardly to the position as shown in Figure 2 and nofurther.

Figure 3 shows the parts after the top plate 26 has been removed asdescribed. The bottom plate 25 cannot so readily be removed from thepressed disk 22a with the plug 21 in this position, as the disk and themold plate stick together. Referringnow to Figure 4, we invert the partsshown in Figure 3 and provide a new bottom plate 3| of somewhat largersize but with a central hole the same as that of the plates 25 and 23.We now locate this new bottom plate 3| in position, as shown in Figure4, and by means of a pressing operation we press the plug 21 downwardlyVuntil the parts occupy the position shown in Figure 5. All these plugpressing operations may be readily performed in any hydraulic or silicagrain and ceramic bond, there being a central plug 21 of a length equalto the combined thickness of plate 3| and disk 22a which has never beenremoved from the central hole in the disk 22a although it has beenpushed back and forth therein.

Y By reason of the procedure indicated, the disk 22a is handled withminimum danger of breakbe readily calculated by those skilled in thisart.

Referring nowxto Figure 1, we provide a mold comprising a mold ring, notshown, a bottom plate 25, a top plate 28, and a central plug 21.. Weplace in thismold a measured quantity of non-diamond containing mixture,as described above, and press in accordance with well-known practice.ring and there exists between mold plates 25 and 26 a green pressed disk22a of non-diamond containing material. Referring now to Figure 2, wenext press the coreV 21 downwardly until it absolutely clears the topplate 26. This permits the top plate 26 to be removed without injuringthe pressed product 22a in any manner whatsoever as it can be slid oil?.After'a pressing operation involving many thousand pounds to the squareinch, both the top and the bottom plates stick to the pressed materialthereof and have to be removed by relative movement in the nature of ashear in order not to destroy the pressed article. It is desired toloosen both top and bottom plates from the pressed article 22a and atthe same time we desire not to remove the plug We then strip the moldfrom the mold ing off any portion thereof. Referring now to Figure 8, Weprovide second molding and pressing apparatus including an upper pressplunger 35, a lower press plunger 36 and a mold ring 31 of specialcharacteristics, to be hereinafter described. Referring now to Figure7,- we now place the bottom plate 3| inside the mold ring 31. Bottomplate 3| fits in the mold ring 31 with a sliding fit, preferably areasonablyy tight t. As shown in Figure '7, the disk 22a is still inposition on the bottom plate 3|. The best manner of introducing the disk3| into the ring 31 is to lower the plunger 35 until the plate 3| can bemoved into position, clearing all obstructions, carefullycentering itand then moving upwardly the plunger 36. The press which may be used inpracticing this invention is not found illustrated in detail ashydraulic presses are well known, and we utilize a hydraulic presshaving low and high pressure in order that the low pressure may be usedwhen it is desired to-bring parts into position and the high pressuremay be used when actually pressing the mixtures. Low pressure is used inelevating the plunger 36 to introduce the bottom plate 3|.

21 at any time entirely from the central hole of We now take themeasured quantity of diamond abrasive and 'bond prepared as abovedescribed and tamp it into the space between the mold ring 31 and thedisk 22a, this diamond abrasive ceramic bonded material being indicatedat 21aln Figure 7. We then place in position a top mold plate 4| whichisshown in Figure'. This plate may have a bayonet slot 42 for readyhandling thereof. We now bring the plunger 35 downwardly with lowpressure and the apparatus is ready for the second molding operation.

Still referring to Figure 8, the mold ring 31 is preferably made of caststeel and has an .annular chamber 33 opening into an inner peripheralslot M extending all the way around thefmold ring. *The mold ring is anintegral piece of great strength. Excepting for the slot 44, chamber 43has only two entrances, viz. an opening 45 in the form of a tapped holeconnected to asteel pipe 46 of great strength with a small bore. 'I'heother opening is another tapped hole 41 closed by screw plug 48. Themold ring 31 has an integral radial ange 50 in which is located adepression l to receive the pipe 46. A series'of massive rods 52 arelocated around the periphery and extend through the flange 50 and aresecured thereto and to a reinforcing ring 53 by means of nuts 54 fittingon threaded portions 55 of the rods 52. These rods 52 extend downwardlyfrom a portion of the hydraulic press mechanism, not shown, and aresuitably anchored thereto. The construction shown constitutes a moldring 31 of great strength able to resist all ordinary forces in eithervertical vdirection and` having an annular chamber 43 able to holdenormous pressures.

In the chamber 43 and extending through the annular slot 4t is anannular rubber ring 60 of uniform cross section around the circle and ofT shape in cross section, as shown. The corners of the junction betweenthe chamber 43 and the slot d4 are rounded, as shown, and so also is therubber at that point. Rubber is a deformable but not compressiblesubstance and when subjected to comparatively large pressures owspractically like a liquid. Simultaneously We introduce high pressurethrough the pipe 46 and against the press plungers 35 and 36. This maybe done by operating three high pressure valves from a single lever. Theupper and lower press plungers 35 and 35 are provided in order that theenormous pressures which are preferably used to compact the material maynot split the mold ring 31 open. We prefer to use pressures of the orderof 6000 lbsfto the square inch. Difference in thrust of the plungers 35and 36 owing to the weight thereof is readily taken care of by thesupporting structure for the mold ring. When this pressure is applied inthe manner indicated, the mixture Zia is compacted to the conditionshown at 2lb Figure 8 and all parts of this mixture as well as of thedisk 22a are subjected to the pressure chosen. It will be seen that eventhe plug 68 which seals the opening 41 is backed up by the upper plunger35.

After the full pressure has been turned on for a few moments, it isreleased in all three places diamonds, contracts at a rate close to thatofl no shrinkage cracks appear and the article is an integral one-piecestructure so far as its physical characteristics are concerned and hasno strains therein, one physical characteristic alone excepted, and thatis the abrasive properties of the annular band 2l.

It will be seen that according to the construction shown, the pipe doesnot move during use of the apparatus. A rigid pipe connection to themold ring 31 is made possible by the use of two press plungers, viz. theupper press plunger- 35 and the lower press plunger 35. By using astationary mold ring, leakage of high pressure uid is avoided. Thechamber' 43 may be and preferably is filled with oil at all times, andby reason of the provision 'of the hole d1 and plug 48 it is possible toremove all air from the chamber 43. Notwithstanding these advantageousfeatures, it

is a: relatively simple operation to remove the n 'mold ring 31 and'substitute another one of a different size.

The :duid pressure that enters the chamber 43 is preferably equal to oreven slightly greater than the pressure which was used to compact thedisk 22a. This will insure a given grade hardness of the entire productand the volume percentage of abrasive, bond and pores or granular andthereupon the rubber ring 6@ expands to the position shown in Figure 9.

eral annulus 2lb. Both plungers 35 and 36 are then moved away from thering 31 and a stripping member of slightly less diameter than the bottomplate 3i is now placed in position and the The mixture 2|a,` however, isnow compacted to a pressed periphmaterial, bond and pores will be verynearly constant throughout the mass. Under these conditions of a finalpressing operation -involving a given pressure which is transmitted tothe entire machine, a homogeneous product without strains results.

So far as certain features of the invention are concerned, the apparatusmay be used for molding diamond abrasive in the form of an annulus orring upon any central disk which will withstand,` the vitrifyingtemperature in a ceramic kiln. Certain advantages of the invention maybe achieved replacing the disk 22a with alprered abrasive disk.Furthermore, the apparatus may be used press mixtures including bondsother than ceramic bond.

It will thus be seen that there has been provided by this invention, amethod and an article in which the various objects hereinabove setforthi together with many thoroughly practical advantages aresuccessfully achieved. As vartemperature until the temporary binder hasbeen burned out, thereafter at a temperature in the neighborhood of l000C. in a non-oxidizing atmosphere.

In the shrinkage following the application of the maximum heat, thevitreous silica, having a coeicient of expansion fairly close to that ofious possible embodiments might be'made of the mechanical featuresof theabove invention and as the art herein described might be varied invarious parts, all without departing from the scope of the invention, itis to be understood that all matter hereinbefore set forth or shown inthe accompanying drawing is to be interpreted as il lustrative and notin a limiting sense. I

We claim:

1. Method of making a diamond abrasive wheel comprising preforming acentral disk of granular material and bond, introducing around said diska mixture of abrasive material and bond, and pressing said mixtureradially by pressure derived from radial forces against the disk, thenmaturing both parts in a single maturing operav tion.

2. Method of making an abrasive wheel includume proportion of bond pertotal solids asin the first mixture, first pressing the latter mixtureto form a disk. then placing the mixture of diamondsand bond around saiddisk, pressing the latter material radially by pressure derived fromradial forces, and maturing the entire abrasive wheel in a singlematuring operation. 3. Method of making a vitried diamond abrasive wheelwhich comprises forming a mixture of diamonds with -ceramic bond,forming another mixture of granular material with ceramic bond, pressingsaid latter mixture into the form of a disk, placing the diamond mixtureoutside of said disk in the form oi' an annulus, pressing the annulusupon the disk radiallyby pressure derived 15 from radial forces. andfiring at a temperature to vitrify the entire' mass into a monolithicwheel.

4. The method or making an abrasive wheel comprising the steps ofproviding a central supporting body, placing a mixture of abrasivegrains LOWELL H. MILLIGAN. ROBERT H. LOMBARD.

